The present invention relates to an electric spark machine and an electrode to be used in such electric spark machine as a tool, which is effective in managing information concerning the electrode.
FIG. 8 shows schematically an example of a conventional electric spark machine and FIG. 9 is a side view showing details of a main portion thereof. In FIGS. 8 and 9, a reference numeral 1 depicts a spark machining electrode, 2 a workpiece to be machined by the electrode 1, 3 a machining tank, 4 machining liquid such as insulating oil, etc., filling the machining tank 3. Usually, machining which uses electric spark machine is performed within the machining liquid 4 in the tank 3. A reference numeral 5 depicts a pulse current generator for supplying pulsed current to the electrode 1 and the workpiece 2, 8a depicts a lead screw for moving a main shaft of the spark machine vertically (in Z axis direction), 8c depicts a screw for moving the workpiece 2 in an X axis direction, 9a depicts a servo motor for rotating the lead screw 8a in the Z direction, 9b depicts a servo motor for rotating a lead screw (not shown) for moving the workpiece in the Y direction, 9c depicts a servo motor for rotating the lead screw 8c in the X direction and 10 depicts a numerical control device for controlling operations of the respective servo motors 9a, 9b and 9c according to a machining program.
A reference numeral 11 depicts a head positioned in an upper portion of the electric spark machine, 12 depicts a column which is a frame fixedly supporting the head 11 and 13 depicts a bed which is a base table of the electric spark machine 14b a movable table for moving the workpiece 2 in the Y direction together with the machining tank 3 and 14c represents a movable table for moving the workpiece 2 in the X direction together with the tank 3. Numeral 5 depicts a spindle head which is a center rod of the main shaft of the electric spark machine on a lower end of which an electrode clamper 15a is for provided clamping the electrode 1 through an electrode angle regulation mechanism 19 for rotating the electrode 1 around an axis of the spindle head (C axis direction). A reference numeral 16 depicts an automatic electrode exchange device for replacing the electrode 1 mounted on the main shaft with another electrode, 17 represents an arm for holding the electrode 1 for replacement thereof and 18 represents a magazine rack which can store various electrodes 1. The electrode 1 is mounted on a shank 20 in order to facilitate an automatic replacement of electrode.
In operation, the electrodes 1 fixedly mounted on the respective shanks 20 are preliminarily stored in the magazine rack 18. The magazine rack 18 has a number of storing portions which are numbered serially. The serial numbers are used as instruction numbers from the numerical control device 10 to identify the perspective electrodes 1. Upon receipt of such instruction number from the numerical control device 10, the magazine rack 18 is rotated to a position in which an electrode 1 stored in the correspondingly numbered storing portion can be caught by the arm 17. Then, the arm is extended leftwardly in the drawing, the shank 20 supporting the electrode 1 and pulls it down. Then, the arm 17 rotates in a horizontal plane by 180.degree. and plugs the shank 20 of the electrode 1 into the electrode clamper 15a while moving upwardly. When the electrode clamper 15a clamps the shank 20 of the electrode 1, the arm 17 separates the shank 20 and is returned to its original position.
When the electrode 1 clamped by the electrode clamper 15a is to be returned to the magazine rack 18, the above described operation of the arm 17 is reversed.
Thus, a discharge machining can be performed by the electrode 1 clamped by the electrode clamper 15a according to the machining program preliminarily inputted to the numerical control device 10.
First, the electrode 1 and the workpiece 2 are arranged in facing relation to each other within the machining liquid 4 in the machining tank 3 and pulsed current is supplied from the pulse current generator 5 to the electrode 1 and the workpiece 2. With such pulse current, an intermittent discharge occurs in a machining gap between the electrode 1 and the workpiece 2 by which the workpiece 2 is machined. During the machining, the electrode 1 connected to the Z axis servo motor 9a through the lead screw 8a is moved vertically according to the instruction from the numerical control device 10.
Further, the tables 14b and 14c which are connected to the Y and X servo motors 9b and 9c through the lead screw 8c and the lead screw which is not shown, respectively, are moved in the Y and X directions according to the instruction of the numerical control device 10, so that horizontal relative position of the electrode 1 to the workpiece 2 can be changed arbitrarily.
The electrode 1 can be rotated in the C direction about the axis of the spindle head by the electrode angle regulator 19.
Therefore, by suitably controlling the servo motors 9a, 9b and 9c and the electrode angle regulator 19, a desired portion of the workpiece 2 can be machined to a configuration corresponding to that of the electrode 1.
In order to perform continuous machining by successively exchanging a plurality of different electrodes 1, it is necessary to preliminarily know the position of such electrode. FIG. 10a shows the workpiece 2 and a reference measuring member 90 provided on the magazine rack 18. A reference ball 91 is provided in the vicinity of the workpiece 2, for measuring the electrode position with respect to the workpiece 2. The reference measuring member 90 has roles of providing a reference for measuring a relative position of the workpiece 2 to the reference ball 91 and of providing a reference for measuring the position of each of the electrodes 1.
The position measurement of the respective electrode 1 will be described. First, a position alignment between the reference measuring member 90 and the reference ball 91 is performed as shown in FIG. 11 in which straight lines show rapid feeding of the reference ball 91 with respect to the reference measuring member 90 and undulated lines show low speed feeding of the reference ball 91 to eventually make in contact with the reference measuring member 90.
Then, as shown in FIG. 10b, an alignment of a first electrode 1A is performed by using the reference ball 91. Thereafter, an alignment of a second electrode 1B is performed as shown in FIG. 10c. These aligning operations are preliminarily programmed in the numerical control device 10 by an operator. That is, a position (in three dimensional X-Y-Z coordinates) and an angle C of the electrode for which the alignment is to be performed are assigned by the operator and results of measurements of the respective electrodes 1 are registered in the numerical control device 10 together with electrode numbers thereof.
With the movements of these members, a three dimensional position of the reference ball 91 can be measured.
In positioning each electrode 1, numerical values to be inputted to the numerical control device 10 may include those indicative of the size of electrode and reference points thereof. When the electrode 1 has a simple configuration such as shown in FIG. 12, for example, positions of faces Xa and Xb of the electrode in the X direction, faces Ya and Yb thereof in the Y direction and face Za thereof in the Z direction are picked up by the reference measuring member 90 in sequence starting from that shown in FIG. 13a to that shown in FIG. 13e.
In such conventional electric spark machine, there is a problem that the machine stops its automatic positioning operation when the operator makes a simple error of inputting correct electrode size to the numerical control device erroneously or inputting erroneous electrode size.
Further, the larger the number of electrodes to be used in a machining requires the longer the time necessary to perform the alignment operation.
For example, Japanese Kokai (P) 146638/1989 discloses an electric spark machine tool whose tool houses a memory capable of being preliminarily read in an information including diameter, length, amount of correction, duration of usage and times of usage of the tool, etc., and which can perform an automatic management of the tool duration. However, such machine tool has no automatic off-center correction for the tool, requiring a lot of time for alignment operation of the tool.
An object of the present invention is to provide an electrode for use in an electric spark machine, with which an automatic misalignment measurement of the electrode mounted on the electric spark machine tool becomes possible, resulting in a substantial improvement on the workability of the machine tool.
Another object of the present invention is to provide an automatic alignment device for positioning electrode correctly with respect to a workpiece.
Another object of the present invention is to provide an electric spark machine using such electrode.